首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   11400篇
  免费   315篇
  国内免费   455篇
系统科学   410篇
丛书文集   344篇
教育与普及   223篇
理论与方法论   66篇
现状及发展   72篇
研究方法   47篇
综合类   11006篇
自然研究   2篇
  2024年   67篇
  2023年   130篇
  2022年   196篇
  2021年   218篇
  2020年   140篇
  2019年   39篇
  2018年   83篇
  2017年   85篇
  2016年   87篇
  2015年   232篇
  2014年   304篇
  2013年   281篇
  2012年   366篇
  2011年   396篇
  2010年   344篇
  2009年   464篇
  2008年   507篇
  2007年   567篇
  2006年   406篇
  2005年   426篇
  2004年   330篇
  2003年   296篇
  2002年   321篇
  2001年   353篇
  2000年   403篇
  1999年   663篇
  1998年   534篇
  1997年   618篇
  1996年   512篇
  1995年   442篇
  1994年   423篇
  1993年   343篇
  1992年   334篇
  1991年   317篇
  1990年   262篇
  1989年   228篇
  1988年   207篇
  1987年   129篇
  1986年   81篇
  1985年   30篇
  1984年   3篇
  1983年   2篇
  1958年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
子波变换新方法   总被引:1,自引:0,他引:1  
本文在理论分析子波变换物理概念的基础上,提出了一种工程上应用的新颖快速子波变换算法,即“频谱切割法”。该方法能够在电路上实现实时的快速子波变换。  相似文献   
72.
Constacyclic codes are an important class of linear codes in coding theory.Many optimal linear codes are directly derived from constacyclic codes.In this paper,(1 — uv)-constacyclic codes over the local ring Fp + uFp + vFp + uvFp are studied.It is proved that the image of a(1 — uv)-constacyclic code of length n over Fp + uFp + vFp + uvFp under a Gray map is a distance invariant quasi-cyclic code of index p2 and length p3n over Fp.Several examples of optimal linear codes over Fp from(1 — uv)-constacyclic codes over Fp + uFp + vFp + uvFp are given.  相似文献   
73.
司法实践中对火灾事故认定的行政可诉性存在较大争议,笔者通过分析行政诉讼法意义上具体行政行为内涵.结合新修订的<消防法>和公安部<火灾事故调查规定>的相关规定,明确火灾事故认定是鉴定结论和处理纠纷的证据,不具备可诉性,并根据证据规则对火灾事故认定工作提出确实可行的建议.  相似文献   
74.
We developed a parallel object-relational DBMS named PORLES. It uses BSP model as its parallel computing model, and monoid calculus as its basis of data model. In this paper, we introduce its data model, parallel query optimization, transaction processing system and parallel access method in detail.  相似文献   
75.
De Casteljau algorithm and degree elevation of Bézier and NURBS curves/surfaces are two important techniques in computer aided geometric design. This paper presents the de Casteljau algorithm and degree elevation of toric surface patches, which include tensor product and triangular rational Bézier surfaces as special cases. Some representative examples of toric surface patches with common shapes are illustrated to verify these two algorithms. Moreover, the authors also apply the degree elevation of toric surface patches to isogeometric analysis. And two more examples show the effectiveness of proposed method.  相似文献   
76.
Confined low dimensional charges with high density such as two-dimensional electron gas (2DEG) at interfaces and charged domain walls in ferroelectrics show gre...  相似文献   
77.
For forecasting nonstationary and nonlinear energy prices time series, a novel adaptive multiscale ensemble learning paradigm incorporating ensemble empirical mode decomposition (EEMD), particle swarm optimization (PSO) and least square support vector machines (LSSVM) with kernel function prototype is developed. Firstly, the extrema symmetry expansion EEMD, which can effectively restrain the mode mixing and end effects, is used to decompose the energy price into simple modes. Secondly, by using the fine‐to‐coarse reconstruction algorithm, the high‐frequency, low‐frequency and trend components are identified. Furthermore, autoregressive integrated moving average is applicable to predicting the high‐frequency components. LSSVM is suitable for forecasting the low‐frequency and trend components. At the same time, a universal kernel function prototype is introduced for making up the drawbacks of single kernel function, which can adaptively select the optimal kernel function type and model parameters according to the specific data using the PSO algorithm. Finally, the prediction results of all the components are aggregated into the forecasting values of energy price time series. The empirical results show that, compared with the popular prediction methods, the proposed method can significantly improve the prediction accuracy of energy prices, with high accuracy both in the level and directional predictions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
78.
79.
We have recently described two kindreds presenting thoracic aortic aneurysm and/or aortic dissection (TAAD) and patent ductus arteriosus (PDA) and mapped the disease locus to 16p12.2-p13.13 (ref. 3). We now demonstrate that the disease is caused by mutations in the MYH11 gene affecting the C-terminal coiled-coil region of the smooth muscle myosin heavy chain, a specific contractile protein of smooth muscle cells (SMC). All individuals bearing the heterozygous mutations, even if asymptomatic, showed marked aortic stiffness. Examination of pathological aortas showed large areas of medial degeneration with very low SMC content. Abnormal immunological recognition of SM-MHC and the colocalization of wild-type and mutant rod proteins in SMC, in conjunction with differences in their coimmunoprecipitation capacities, strongly suggest a dominant-negative effect. Human MYH11 gene mutations provide the first example of a direct change in a specific SMC protein leading to an inherited arterial disease.  相似文献   
80.
Tan L  Li X  Liu F  Sun X  Li C  Zhu Z  Fu Y  Cai H  Wang X  Xie D  Sun C 《Nature genetics》2008,40(11):1360-1364
The transition from the prostrate growth of ancestral wild rice (O. rufipogon Griff.) to the erect growth of Oryza sativa cultivars was one of the most critical events in rice domestication. This evolutionary step importantly improved plant architecture and increased grain yield. Here we find that prostrate growth of wild rice from Yuanjiang County in China is controlled by a semi-dominant gene, PROG1 (PROSTRATE GROWTH 1), on chromosome 7 that encodes a single Cys(2)-His(2) zinc-finger protein. prog1 variants identified in O. sativa disrupt the prog1 function and inactivate prog1 expression, leading to erect growth, greater grain number and higher grain yield in cultivated rice. Sequence comparison shows that 182 varieties of cultivated rice, including 87 indica and 95 japonica cultivars from 17 countries, carry identical mutations in the prog1 coding region that may have become fixed during rice domestication.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号